Returning to the OP, I agree that there is some truth that is axiomatic/unavoidable/inescapable, because in order to study reality it appears that one must (logically or implicitly) begin by assuming at least the reality of the student. Thus, absolute skepticism in philosophy is like absolute zero in physics: it serves as a hypothetical point that is not actually achieved or else nothing would happen.
The truth represented by skepticism is that finite human beings cannot know absolutely, infallibly, perfectly or objectively. I find this truth expressed by the apostle Paul in the New Testament (NT) book of 1 Corinthians 13:9&12, “We know in part . . . We see but a poor reflection” (as in a fogged mirror). However, the element of uncertainty does not prevent would-be skeptics from talking as if knowledge with some degree of confidence were possible the moment they attempt to communicate their doubts. An agnostic has “certain” assumptions at least implicitly: that truth is believable, rational and meaningful, even though unprovable or subjective.
These three affirmations seem to be a priori truth or unavoidable (beginning) beliefs:
1. Truth or reality exists. The classic expression of this belief was by Rene Descartes (d.1650): cogito ergo sum: “I think, therefore I am” (cf. Rodin’s sculpture; thinking is believing). The Old Testament (OT) says in Exodus 3:14 that God is “I am” (the essence of existence).
2. (Objective) reality is subjectively known by seekers. David Hume (d. 1776) was a notable proponent of this opinion, and 2 Corinthians 5:7 expresses this truth by saying, “We live by faith, not by sight” (or proof, cf. 1CR 13:9&12 cited previously). [From this point biblical books in parentheses will be abbreviated.]
3. Reality is meaningful and communicable or able to be discussed rationally in fellowship with other truthseekers. As Isaiah 1:18a (c.735 B.C.) says, “Come now, let us reason together.” Perhaps whoever invented language should be regarded as the founder of this fact, because the discussion of reality uses language as the means, and in order to communicate sufficiently for attaining agreement or unity, it is necessary to have a common language and cultural context. (I hope that as Earthlings using English these needs are met for you and me :^)
Having established three unavoidable or axiomatic beliefs, what is the logical point from which the varieties of beliefs extant in the world diverge? Only the first student or one with a tabula rasa (blank slate)—like a newly sentient child—actually starts exploring reality from the beginning, (a pre-sentient infant in the womb is completely agnostic or without knowledge of every ism), so we must “begin” by seeking to assume the position or condition of adult innocence (unprejudice).
Imagining that we have suddenly begun to exist as a mentally competent or normally intelligent human being (like Adam and Eve in Genesis), certainly, our immediate concern would be meeting survival needs, but as soon as there was time for reflection, would we not wonder why we were “born”, how we should behave, and what we ought to accomplish with your life? Since absolute skepticism or agnosticism is unattainable for thinkers or truthseekers, there are only [IOW, volition is limited to choosing between only] two qualitatively different ways of answering these questions.
One way is by assuming that there is no ultimate “whyness” or purpose beyond survival and avoiding pain, so it does not ultimately matter what one believes or does, because humanity merely evolved from eternal energy/matter, into which it “devolves” at death. You may desire for some reason to survive and to save the world, but if life becomes too painful you may wish you were never born and want to destroy the world, because there is no good reason you ought to be like Messiah rather than like Mania or to be loving rather than maniacal. You may believe and act like evil exists or not, because life is a farce or a continual “King of the Hill” (KOTH) struggle against human adversaries and various other types of adversity, having no ultimate or universal moral imperative (UMI).
The second type of answer is that life is NOT a farce—that existence has meaning, and how one believes and behaves does matter for some non-arbitrary reason. This answer seems more appealing to me and almost logically imperative, although some people appear to prefer the path of nihilism (cf. MT 13:14-15).
I call the first type of answer cosmaterialism, because it views reality as consisting only of the material cosmos or universe and as having only four dimensions (space plus time), which are perceived by the five physical senses. I call the second way of believing moralism, because—while accepting the reality of the physical/material—it also affirms a fifth dimension perceived by a sixth intuitive or spiritual sense that gives reality a logical (cf. Logos) basis for meaning and morality.
The choice between cosmaterialism and moralism logically is the first fundamental choice in life (cf. GN 3:5). It can be thought of as a watershed decision that divides all people into two essentially different philosophical categories or world-views like a continental divide, although the analogy breaks down at the points the various oceans connect. A person who believes cosmaterialism, moral nihilism and that life’s struggles are meaningless frequently tends to seek escape even via suicide, whether by one act or by a downward spiral of self-destructive behavior. Again, until and unless this option were somehow proven beyond doubt, moralism or viewing life as meaningful seems to be the better belief/choice.
(As Christians, we have chosen moralism :^)